Musical instrument with electric sound reproduction system



March 3, 1936. N. A. 'PALMGREN MUSICAL INSTRUMENT WITH ELECTRIC SOUNDREPRODUCTION SYSTEM Filed July 16, 1952 INVENTOR ATTORNEY /V/1 s ARV/oPALM'GRE/V Patented Mar. 3, 1936 PATENT OFFICE MUSICAL INSTRUMENT WITHELECTmo SOUND REPRODUCTION SYSTEM Nils Arvid Palmgren, Goteborg, SwedenApplication July 16, 1932, Serial No. 622,993 In Sweden February 8, 19321 Claim. (Cl. 84-1 The present invention relates to musical instrumentsassociated with electric sound reproduction systems and is applicable toall types of instruments having a series of mechancal vibratory systemsor vibratory bodies, such as strings, or the like, tuned to acousticfrequencies and consisting wholly or in part of electrically conductivematerial.

.An object of the invention is to provide an instrument having a widerrange both as to volume and timbre than hitherto known types, and whichwill, therefore, permit the volume and timbre of the difierent tones tobe adapted to the most varied requirements.

A further object of the invention is to provide an instrument which canbe inexpensively manuiactured and which will he of light weight andrequire but small space.

wan these and other objects in view the invention consists mainly inthat one or more electrodes or the like are disposed near the vibratorybodies and electrically insulated from them, so

that the electrodes form electrical condensers together with thevibratory bodies.

Several forms of the invention are illustrated in the accompanyingdrawing, in which:

Figure, 1 shows in diagram the principle of the electrical part of theinstrument.

Fig. 2 is a diagram of a form of the invention, the mechanicalarrangement of whichv is illustrated in Figs. 3, 4 and 5;

3 being a vertical section through the instrument,

Fig. 4 a section along the line 5-4 in Fig. 3 and Fig. 5 a section alongthe line 5-5 in Fig. 3.

Referring now to Fig. 1, the numeral i denotes a body capable of beingset in vibration. Near the body I is an electrically conductive body, or

electrode, 2 which is electrically insulated from the vibratory bodythrough an air gap, and thus together with this body forms an electricalcondenser. The body I is in a suitable manner connected to a sourceofelectric energy 4, for instance a generator, a battery or the like.The electrode 2 is connected to a resistance 3 offering a relativelygreat impedance to alternating current. The resistance and the source ofenergy are connected in the manner shown in the diagram so that theelectric capacity of the condenser formed by the vibratory body and. theelectrode will form part of an electric circuit in series with theresistance. Ii the vibratory body is now set in vibration, there will bea flow of electrons to and from the electrode 2 in a similar manner asin a capacitance microphone. This current will give rise to a variationin potential between the terminals 5 and 6 of the resistance 3.

In the form of the invention illustrated in Fig. 2, two sections ofelectrodes 2 and 2 are disposed near the vibratory body I and eachcovers a part of this body. Either one of these elec trodes, or bothsimultaneously, can be connected to the primary or" an audio frequencytransformer 8 by the battery 1. The secondary oi the transformer isconnected to a resistance 9 from which a movable contact ill leads tothe terminal 5. Any desired voltage can thus be obtained between theterminals 5 and 6.

The above described circuit diagram is shown applied to the form of theinvention illustrated in 1 Figs. 3, 4.- and 5. in this form of theinvention a number of strings l are mounted under tension on a frame it,in such a manner that they can be tuned to different audiblefrequencies. The strings can caused to vibrate by blows from hammers l2manipulated from the keys ll. Behind the strings are disposed twoelectrode sections 2 and 2 These electrode sections together cover thegreater part of the length of the strings, and the fundamentalvibrations of the strings will, therefore, cause great variations incapacity. On the other hand, the variations in capacity due to theharmonics will be very small. Especially will this be so for the evenharmonics. This will result in a softer tone and a deeper timbre thanthat of the tone emitted directly by the string. A tone, in which theharmonics are louder relative to the fundamental, is obtained if theelectrode covers only a portion of the length of the string at thevicinity of the end of the string, as all harmonics have a common nodeat the end of the string, while the only anti-node of the fundamental issituated at the middle of the string. If, for instance, only the section2* is connected, the four first harmonics will be very pronounced andwill be even louder relative to the fundamental than when transmitteddirect to the ear from the string. If only the section 2 of theelectrode is active mainly the fundamental and the second harmonic willbe amplified. The timbre of the instrument can, therefore, be altered bymeans of the two-way switch IS. The arm of the two-way switch isconnected to the transformer 8, which is in its turn connected to thebattery 1. The other pole of the battery is electrically connected toall the strings I. The potentiometer 9 is connected across the secondaryof the transformer, The movable contact III of the potentiometer isactuated from a pedal l3 so that, when the pedal is It is apparent fromFig. 8 that the electrode,

section 2" for example covers a diflerent pro--, portion of the lengthof the diflerent strings: In this manner it is possible to accentuatethe harmonics of strings relatively lacking in harmonics and to dampthem instrings richer in harmonics. As illustrated in Fig. 3, 29% of thelength of the shortest string, but only 24% o! the length of the longeststring, is covered by the electrode 2 Fig. 4 shows how the distancebetween the string and the electrode can be varied along the length ofthe same string. The distance is small at the bottom of the string andgreater at the top. In this manner it is possible to adjust the relativesound volumes when connecting the different electrode sections or toadjust the volume of a certain harmonic, or certain harmonics,

relative to the fundamental.

Fig, 5 illustrates the manner in which the distance between the stringsand the electrode electrode has no resonance in the acoustic trequencyrange or that its resonance is so suppressed that it will be aperiodic.In the special iorm of the invention described above it should be notedthat the transformer 8 should have a high primary inductance and lowcapacity between the turns in order to obtain the greatest possiblevolume. 1

It only the electrode 2" is used, the additional advantage is obtainedin the form or the invention described that the hammers I 2 strike thestrings at a part not covered by an active electrode.

Having thus described my invention, what I claim and desire to secure byLetters Patent is:

In a musical instrument, the combination of a plurality of tuned,electrically conductive strings; means for vibrating said strings attheir respective fundamental and partial frequencies, an. electrodepositioned adjacent to said strings and forming electrical capacitieswith said strings, the electrode uninterruptedly covering a greater partof each string in which part the string vi- 343

